Various facilities such as lighting, air-conditioning, and disaster preventing facilities are installed in buildings. In order to realize controlling these facilities from the inside or outside of the buildings or monitoring if abnormalities have occurred or not, a device and a system that remotely collect working information (process data) of the building facilities over a network have been proposed. In such a system, the process data are transferred via a network between an information collecting device and building-side communicating devices, which are connected to the building facilities of interest to collect information from them. The process data are generally collected at a certain determined time cycle, because such data are easier to utilize than data collected irregularly.
When the building facilities the system collects information from are increased, the communication traffic between the building-side communicating devices and the information collecting device is increased. When the communication traffic is increased to the extent close to a communication bandwidth, problems such as loss of the data communicated over the network and increase in the delay generated in process data acquisition occur. Therefore, there has been proposed a method in which the cycle to acquire the process data is determined in accordance with the communication bandwidth or importance of the facility information. For example, a long acquisition cycle is set for a building-side communicating device having a small communication bandwidth.
According to this method, an average volume of the communication traffic can be limited to a predetermined value by adjusting the acquisition cycle. However, in this method, the time to acquire the process data is not controlled; therefore, large communication load may be momentarily generated on the information collecting device or the building-side communicating device. For example, even in the case in which the acquisition cycle of the process data is sufficiently large, if the information collecting device attempts to acquire data from many building facilities at the same time, communication load that exceeds the communication bandwidth or processing ability of the information collecting device can be momentarily generated.
In order to solve these problems, there has been proposed a method in which the time to carry out communication is determined in advance for each of building-side communicating devices. In this method, the acquisition cycle of the process data is divided into certain unit periods. A communication event between the building-side communicating devices and the information collecting device is assigned to one of these unit periods. When such a method is employed, an upper limit can be set for the number of the building-side communicating devices that communicate within the unit period; therefore, momentary traffic concentration at the information collecting device can be prevented.
However, in this method, the communication load applied to the building-side communicating devices is not controlled. Therefore, even though the concentration of the communication load on the information collecting device can be prevented, the possibility of the momentary occurrence of excessive communication load for the building-side communicating devices is still remaining.
As described above, when the process data are to be collected at a constant cycle, excessively large communication load may be concentrated on the information collecting device or the building-side communicating device. The concentration of the communication load applied only to the information collecting device can be prevented; however, a device or a system capable of preventing the communication load concentration both on the information collecting device and the building-side communicating device is not present.